Air bags are being increasingly installed in motor vehicles for the purpose of reducing the impact on the human-body during a collision accident involving an automobile or other motor vehicle. Air bags absorb and reduce the impact on the human-body by being inflated by a gas at the time of a collision, and in addition to air bags for the driver's seat and passenger's seat, air bags such as curtain air bags, side air bags, knee air bags and rear air bags are being installed and used practically throughout vehicles to ensure passenger protection. Moreover, air bags have also been proposed that are installed so as to inflate outside the passenger compartment in order to protect pedestrians.
Air bags such as curtain air bags, which are deployed and inflated from the ceiling above the doors to protect the head and neck regions of passengers during a side collision, or side impact air bags, which are deployed and inflated from the car seats to protect the chest and pelvis of passengers, are required to cushion the body by being deployed at high speed due to the short distance between the vehicle sidewall and the occupant's body. In addition, since air bags for protecting pedestrians cover a large area, they are also required to prepare for a collision by being deployed at high speed.
These air bags are folded up and stored in a compact form during ordinary vehicle operation. When a collision has been detected by a sensor and the air bag deploys and inflates, the air bag flies out by breaking through its storage compartment, such as the fitting of a ceiling trim cover or the stitched portion of a passenger seat, while being unfolded by gas generated with an inflator to cushion the human-body when it has been sufficiently inflated.
In the case of air bags that are required to deploy at higher speeds, it is necessary to enhance the pressure resistance of the bag-shape article in order to obtain an air bag that offers a higher level of safety. Therefore, the need has arisen to suppress air permeability under high-pressure conditions to a greater extent than in the past. Moreover, it is also necessary to suppress high-pressure air permeability even after exposure to heat in order to maintain performance over a long period of time.
Although a method involving providing a resin coating on a fabric has been used to suppress air permeability, a lightweight fabric free of a resin coating is advantageous for high-speed deployment.
For example, Patent Document 1 indicated below discloses a textile for an air bag in which air permeability at a pressure difference of 500 Pa is 120 L/dm2·min or less even after aging cycle treatment, consisting of subjecting to a high temperature of 105° C. for 100 hours followed by subjecting to a low temperature and high humidity, and the change in air permeability after aging cycle treatment is 15% or less, and discloses as the production method of that textile a process consisting of subjecting to shrinkage treatment in hot water at 60° C. to 140° C. and drying in a tender at a temperature of 150° C. or lower followed by cooling slowly and winding at low tension.
Patent Document 2 indicated below discloses a textile in which air permeability at a pressure difference of 500 Pa or less is 120 L/dm2·min or less even after high-temperature treatment at 120° C. for 400 hours by using a textile processing step consisting of multistage heated drying following hot water shrinkage. In addition, Patent Document 3 indicated below discloses a textile in which air permeability at a pressure difference of 19.6 kPa is 0.50 L/cm2/min or less even after high-temperature treatment at 120° C. for 400 hours by subjecting a textile, which uses a multifilament yarn having a filament fineness of 1 dtex to 2 dtex, to high-temperature setting, with the rate of change before and after treatment being 150% or less. However, air permeability under even higher pressure conditions during air bag deployment and high-pressure air permeability following exposure to heat are not disclosed. In addition, high-pressure air permeability after an air bag has been exposed to heat after having been folded up and housed in a compact compartment is also not disclosed.